Multi-generator system for an ultrasonic processing tank

ABSTRACT

The invention provides systems, methods and apparatus for processing delicate parts within a process tank such as an ultrasonic tank. Typically, one or more transducers connect to the tank and respond to drive signals from a generator to produce ultrasound within process liquid within the tank. Specific features of the invention include: (1) a power up-sweep ultrasonic system for moving contaminants upwards within the tank by sweeping transducer drive signals from an upper frequency to a lower frequency without sweeping from the lower frequency to the upper frequency; (2) a multi-generator system for producing ultrasound at selected different frequencies within the tank by switching a common transducer bank to one of the generators in response to remote relays initiated by the user; (3) a probe sensing system for sensing process conditions within the tank including an enclosure for housing a sample liquid and one or more sensing transducers within the sample liquid, the transducers generating signals indicative of characteristics of the sample liquid, a subsystem analyzing the signals in feedback with the generator to modify process conditions; (4) variable voltage ultrasonic generator systems to accommodate varying world-wide voltage supplies; (5) a laminar process tank for efficiently pushing contaminants upwards in a tank; (6) a quick dump rinse tank including a pressure cavity to accelerate dumping processes; (7) an ultrasonic generating unit formed of a printed circuit board (PCB) and multiple transducers within the PCB; (8) an AC power system to produce an AC voltage at frequency f that is impressed across a capacitive element; and (9) various configurations of transducers, including acid-safe transducers, double-compression transducers, and transducers with increased reliability.

RELATED APPLICATIONS

The subject application is a continuation-in-part of commonly-owned U.S.patent application Ser. No. 09/370,302 filed Aug. 9 1999; now U.S. Pat.No. 7,004,016 which is a division of U.S. patent application Ser. No.09/097,374 filed Jun. 15, 1998 (now U.S. Patent No. 6,016,821, grantedJan. 25, 2000); which is a continuation of U.S. patent application Ser.No.: 08/718,945 filed Sep. 24, 1996 (now U.S. Pat. No.: 5,834,871,granted Nov. 10, 1998) and U.S. Provisional Application No.: 60/049,717filed Jun. 16, 1997).

BACKGROUND OF THE INVENTION

Ultrasonic systems for processing and cleaning parts are widely used byindustry. Such systems typically include (a) a tank to hold the processchemistry such as cleaning solution, (b) an ultrasound generator, and(c) one or more transducers connected to the tank and the generator todeliver ultrasound energy to the process chemistry. These systems aregenerally adequate for low frequency operation, i.e., where the energyapplied to the chemistry is around 20 khz. However, prior art ultrasoundprocessing equipment has important technology limitations when operatingat high frequencies and high power; and delicate parts such as diskdrives for the computer industry require high frequency, high powerultrasound in order to effectively process components without damage. Inone failure mode, for example, prior art transducers are known to failwhen subjected to extended periods of operation, especially at highfrequency and high power. In addition, prior art transducers aregenerally non-linear with respect to power output as a function of drivefrequency. Therefore, prior art ultrasonic processing systems sometimesinclude costly electronics to compensate for such non-linearities.

There are other problems. For example, certain manufacturers requirethat a particular generator be matched to a particular tank since thatcombination is measured and known to provide particular processcharacteristics. However, this is cumbersome to an end user who cannotswap one generator for another in the event of a failure. Moreimportantly, though, end users are not able to effectively monitorwhether the system has degraded. Typically, for example, end usersbecome aware of failure modes only after parts are damaged or destroyedwithin the process. There is a need, therefore, of monitoring systemswhich monitor processes in real-time.

It is, accordingly, one object of the invention to provide systems,apparatus and methods for delivering high frequency, high powerultrasound energy to process chemistries. Another object of theinvention is to provide generators and systems which enablemulti-frequency operation, selectively and without undue difficulty.Still another object of the invention is to provide improved transducerdesigns which increase system reliability and which improve powerdelivery. Yet another object of the invention is to provide systems,apparatus and methods for monitoring ultrasound processes in real-timeor as a quality control (“QC”) step.

SUMMARY OF THE INVENTION

As used herein, “ultrasound” and “ultrasonic” generally refer toacoustic disturbances in a frequency range above about eighteenkilohertz and which extend upwards to over two megahertz. “Lowerfrequency” ultrasound, or “low frequency” ultrasound mean ultrasoundbetween about 18 khz and 90 khz. “Megasonics” or “megasonic” refer toacoustic disturbances between 600 khz and 2 Mhz. As discussed above, theprior art has manufactured “low frequency” and “megasonic” ultrasoundsystems. Typical prior art low frequency systems, for example, operateat 25 khz, 40 khz, and as high as 90 khz. Typical prior art megasonicsystems operate between 600 khz and 1 Mhz Certain aspects of theinvention apply to low frequency ultrasound and to megasonics. However,certain aspects of the invention apply to ultrasound in the 100 khz to350 khz region, a frequency range which is sometimes denoted herein as“microsonics.”

As used herein, “resonant transducer” means a transducer operated at afrequency or in a range of frequencies that correspond to a one-halfwavelength (λ) of sound in the transducer stack. “Harmonic transducer”means a transducer operated at a frequency or in a range of frequenciesthat correspond to 1λ, 1.5λ, 2λ or 2.5λ of sound, and so on, in thetransducer stack. “Bandwidth” means the range of frequencies in aresonant or harmonic region of a transducer over which the acousticpower output of a transducer remains between 50% and 100% of the maximumvalue.

As used herein, a “delicate part” refers to those parts which areundergoing a manufacture, process, or cleaning operation within liquidsubjected to ultrasonic energy. By way of example, one delicate part isa semiconductor wafer which has extremely small features and which iseasily damaged by cavitation implosion. A delicate part often definescomponents in the computer industry, including disk drives,semiconductor components, and the like.

As used herein, “khz” refers to kilohertz and a frequency magnitude ofone thousand hertz. “MHz” refers to megahertz and a frequency magnitudeof one million hertz.

As used herein, “sweep rate” or “sweep frequency” refer to the rate orfrequency at which a generator and transducer's frequency is varied.That is, it is generally undesirable to operate an ultrasonic transducerat a fixed, single frequency because of the resonances created at thatfrequency. Therefore, an ultrasonic generator can sweep (i.e., linearlychange) the operational frequency through some or all of the availablefrequencies within the transducer's bandwidth at a “sweep rate.”Accordingly, particular frequencies have only short duration during thesweep cycle (i.e., the time period for sweeping the ultrasound frequencythrough a range of frequencies within the bandwidth). “Sweep the sweeprate” or “double sweeping” or “dual sweep” refer to an operation ofchanging the sweep rate as a function of time. In accord with theinvention, “sweeping the sweep rate” generally refers to the operationof sweeping (i.e., linearly changing) the sweep rate so as to reduce oreliminate resonances generated at the sweep frequency.

In one aspect, the invention provides ultrasound transducer apparatus.In the apparatus, at least one ceramic drive element is sandwichedbetween a front driver and a backplate. The drive element has electricalcontacts or electrodes mounted on either face and is responsive tovoltages applied to the contacts or electrodes so as to produceultrasound energy. A connecting element—e.g., a bolt—connects the backplate to the front driver and compresses the drive element therebetween.In accord with the invention, the front driver and/or the backplate areshaped so that the apparatus produces substantially uniform power as afunction of frequency over a range of frequencies. In another aspect,the shape of the driver and/or backplate are selected so as to provide avarying power function as a function of frequency.

In another aspect, a multi-frequency ultrasound generator is provided.In one aspect, the generator includes a constant power output circuitwith means for switching the center frequency of the output signalselectively. The switching means operates such that little or nointermediate frequencies are output during transition between one centerfrequency and another.

Another multi-frequency generator of the invention includes two or morecircuits which independently create ultrasound frequencies. By way ofexample, one circuit can generate 40 khz ultrasound energy; whileanother circuit-can generate 104 khz energy. A switching networkconnects the plurality of circuits such that the generator is shut downand relay switching takes place in a zero voltage condition. As above,therefore, the switching occurs such that little or no intermediatefrequencies are output during transition between one center frequencyand another.

In still another aspect, a two stage ultrasonic processing system isprovided. The system includes (a) one or more transducers with a definedultrasound bandwidth defined by an upper frequency and a lowerfrequency. The system further includes (b) a frequency generator fordriving the transducers from the upper frequency to the lower frequencyover a selected or variable time period and (c) a process tank connectedwith the transducers so as to generate ultrasound energy within the tankat frequencies defined by the generator. During a given cycle, thegenerator drives the transducers from the upper frequency to the lowerfrequency. Once the lower frequency is reached, a frequency controlsubsystem controls the generator so as to drive the transducers againfrom upper to lower frequency and without driving the transducers fromlower to upper frequencies. In this manner, only decreasingfrequencies—per cycle—are imparted to process chemistries. The systemthus provides for removing contamination as the downward cyclingfrequencies cause the acoustic energy to migrate in an upwards motioninside the tank which in turn pushes contamination upwards and out ofthe tank.

In another aspect of the invention, the two stage ultrasonic processingsystem includes means for cycling from upper-to-lower frequencies everyhalf cycle. That is, once the transducers are driven from upper to lowerfrequencies over a first half cycle, the generator recycles such thatthe next half cycle again drives the transducers from upper to lowerfrequencies. Alternatively, after driving the transducers from upper tolower frequencies for a first half cycle, the system inhibits the flowof energy into the tank over a second half cycle.

The two stage ultrasonic processing systems of the invention can becontinuous or intermittent. That is, in one preferred aspect, the systemcycles from upper to lower frequencies and then from lower to upperfrequencies in a normal mode; and then only cycles from upper to lowerfrequencies in a contamination removing mode.

In still another aspect, the invention provides a process control probewhich monitors certain process characteristics within an ultrasonicprocess tank. The probe includes an enclosure, e.g., made frompolypropylene, that transmits ultrasound energy therethrough. Theenclosure houses a liquid that is responsive to the ultrasonic energy insome manner such as to create free radicals and ions from whichconductivity can be measured. This conductivity provides an indicationas to the number of cavitation implosions per unit volume being impartedto the process chemistry within the tank. A conduit from the enclosureto a location external to the process chemistry is used to measure thecharacteristics of the liquid in response to the energy. In otheraspects, a thermocouple is included within the enclosure and/or on anexternal surface of the enclosure (i.e., in contact with the processchemistry) so as to monitor temperature changes within the enclosureand/or within the process chemistry. Other characteristics within thetank and/or enclosure can be monitored over time so as to createtime-varying functions that provide other useful information about thecharacteristics of the processes within the tank.

In one aspect, the invention provides an ultrasonic system for movingcontaminants upwards within a processing tank, which holds processliquid. An ultrasonic generator produces ultrasonic drive signalsthrough a range of frequencies as defined by an upper frequency and alower frequency. A transducer connected to the tank and the generatorresponds to the drive signals to impart ultrasonic energy to the liquid.A controller subsystem controls the generator such that the drivesignals monitonically change from the upper frequency to the lowerfrequency to drive contaminants upwards through the liquid.

In one aspect, the controller subsystem cyclically produces the drivesignals such that the generator sweeps the drive signals from the upperfrequency to the lower frequency over a first half cycle, and from thelower frequency to the higher frequency over a second one half cycle.The subsystem of this aspect inhibits the drive signals over the secondhalf cycle to provide a quiet period to the liquid.

In other aspects, the first and second one-half cycles can havedifferent time periods. Each successive one-half cycle can have adifferent time period such that a repetition rate of the first andsecond half cycles is non-constant. Or, the first one-half cycle canhave a fixed period and the second one-half cycle can be non-constant.

In one aspect, the first half cycle corresponds to a first time periodand the second one half cycle corresponds to a second time period, andthe subsystem varies the first or second time periods between adjacentcycles.

Preferably, the subsystem includes means for shutting the generator offduring the second one half cycle.

In another aspect, the subsystem includes an AM modulator for amplitudemodulating the drive signals at an AM frequency. In one aspect, the AMmodulator sweeps the AM frequency. In another aspect, the AM modulatorsweeps the AM frequency from a high frequency to a low frequency andwithout sweeping the AM frequency from the low frequency to the highfrequency. The subsystem can further inject a quiet or degas periodbefore each monotonic AM frequency sweep.

In another aspect, there is provided an ultrasonic system for movingcontaminants upwards within a processing tank including: a processingtank for holding process liquid, an ultrasonic generator for generatingultrasonic drive signals through a range of frequencies defined betweenan upper frequency and a lower frequency, at least one transducerconnected to the tank and the generator, the transducer being responsiveto the drive signals to impart ultrasonic energy to the liquid, and acontroller subsystem for controlling the generator through one or morecycles, each cycle including monotonically sweeping the drive signalsfrom the upper frequency to the lower frequency, during a sweep period,and recycling the generator from the lower frequency to the upperfrequency, during a recovery period, the sweep period being at leastnine times longer than the recovery period.

In one aspect, the controller subsystem varies a time period for eachcycle wherein the time period is non-constant.

In still another aspect, an ultrasonic system is provided for movingcontaminants upwards within a processing tank, including: a processingtank for holding process liquid; an ultrasonic generator for generatingultrasonic drive signals; at least one transducer connected to the tankand the generator, the transducer being responsive to the drive signalsto impart ultrasonic energy to the liquid; and an amplitude modulationsubsystem for amplitude modulating the drive signals through a range ofAM frequencies characterized by an upper frequency and a lowerfrequency, the subsystem monotonically changing the AM frequency fromthe upper frequency to the lower frequency to drive contaminants upwardsthrough the liquid.

In one aspect, the generator sweeps the drive signals from upper tolower frequencies to provide additional upwards motion of contaminantswithin the liquid.

In another aspect, the AM frequencies are between about 1.2 khz and alower frequency of 1 Hz. The AM frequencies can also cover a differentrange, such as between about 800 Hz and a lower frequency of 200 Hz.

In another aspect, the invention provides a multi-generator system forproducing ultrasound at selected different frequencies within aprocessing tank of the type including one or more transducers. Agenerator section has a first generator circuit for producing firstultrasonic drive signals over a first range of frequencies and a secondgenerator circuit for producing second ultrasonic drive signals over asecond range of frequencies. The generator section has an output unitconnecting the drive signals to the transducers. Each generator circuithas a first relay initiated by a user-selected command wherein eitherthe first or the second drive signals are connected to the output unitselectively.

In one aspect, a 24VDC supply provides power for relay coils.

In another aspect, each generator circuit has a second relay forenergizing the circuit. Two time delay circuits can also be included fordelay purposes: the first time delay circuit delaying generator circuitoperation over a first delay period from when the second relay isenergized, the second time delay circuit delaying discontinuance of thefirst relay over a second delay period after the generator circuit iscommanded to stop. The first delay period is preferably longer than thesecond delay period such that no two generators circuits operatesimultaneously and such that all generator circuits are inactive duringswitching of the first relay.

Each relay can include a 24 VDC coil. A selecting device, e.g., a PLC,computer, or selector switch, can be used to select the operatinggenerator circuit At selection, 24 VDC connects to the two relays ofthis operating generator circuit Preferably, each relay coil operates ata common voltage level.

In one aspect, a variable voltage ultrasonic generator system isprovided, including: an ultrasonic generator; a switching regulator forregulating a 300 VDC signal to +12V and +15V lines, the generator beingconnected to the +12V and +15V lines; and a power factor correctioncircuit connected to AC power. The power factor correction circuitprovides 300 VDC output to the generator and to the regulator. Thegenerator thus being automatically operable from world voltage sourcesbetween 86 VAC and 264 VAC.

In another aspect, a variable voltage ultrasonic generator system isprovided, including: an ultrasonic generator; and a universal switchingregulator (known to those skilled in the art), connected to AC power,for regulating a set of DC voltages to the generator. The generator thusbeing automatically operable from world voltage sources between 86 VACand 264 VAC.

In another aspect, a double compression transducer is provided forproducing ultrasound within an ultrasound tank. The transducer has afront plate and a backplate. At least one piezoceramic is sandwichedbetween the front plate and backplate. A bias bolt with an elongatedbias bolt body between a bias bolt head and a threaded portion extendsthrough the front plate and the piezoceramic and is connected with thebackplate (either by screwing into the backplate or by a nut screwedonto the bias bolt adjacent the backplate). The bias bolt also forms athrough-hole interior that axially extends between the head and thethreaded portion. A second bolt with an elongated body between a secondbolt head and a threaded tip is disposed within the bias bolt. Thesecond bolt head is rigidly attached to the tank and a nut is screwedonto the threaded tip and adjacent to the backplate. The bias bolt thusprovides a first level of compression of the piezoceramic. The secondbolt provides a second level of compression of the front plate and thetank, particularly when epoxy is used to bond between the front plateand the tank.

In still another aspect, a variable voltage ultrasonic generator systemis provided. The system includes an ultrasonic generator and a constantpeak amplitude triac circuit connected to AC power. The triac circuitconverts the AC power to a 121.6 voltage peak, or less, AC signal. Abridge rectifier and filter connects to the AC signal to rectify andfilter the AC signal and to generate a DC voltage less than(86)(√{square root over ( )}2) volts. A switching regulator regulatesthe DC voltage to 12 VDC and 15 VDC; and the generator connects to theDC voltage, the 12 VDC and the 15 VDC. In this manner, the generator isthus automatically operable from world voltage sources between 86 VACand 264 VAC.

The invention is next described further in connection with preferredembodiments, and it will become apparent that various additions,subtractions, and modifications can be made by those skilled in the artwithout departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be obtained byreference to the drawings, in which:

FIG. 1 shows a cut-away side view schematic of an ultrasound processingsystem constructed according to the invention;

FIG. 2 shows a top view schematic of the system of FIG. 1;

FIG. 3 shows a schematic illustration of a multi-transducer systemconstructed according to the invention and used to generate broadbandultrasound in a combined bandwidth; FIG. 4 graphically illustrates theacoustic disturbances produced by the two transducers of FIG. 3; FIG. 5graphically illustrates the broadband acoustic disturbances produced byharmonics of a multi-transducer system constructed according to theinvention;

FIG. 6–16 show transducer and backplate embodiments for systems, methodsand transducers of the invention; and FIG. 17 shows representativestanding waves within one transducer of the invention;

FIG. 18 illustrates preferential placement and mounting of multipletransducers relative to a process tank, in accord with the invention;

FIG. 19 illustrates a representative standing wave relative to theprocess tank as formed by the arrangement of FIG. 18;

FIG. 20 illustrates another preferential pattern of placing transducersonto a mounting surface such as an ultrasound tank, in accord with theinvention;

FIG. 21 illustrates, in a side view, the mounting of two transducers(such as the transducers of FIG. 20) to a tank, in accord with theinvention;

FIG. 22 shows an exploded side view of further features of onetransducer such as shown in FIG. 21;

FIG. 23 illustrates a two stage ultrasound delivery system constructedaccording to the invention; and FIGS. 24 and 25 show alternative timingcycles through which the system of FIG. 23 applies ultrasound from upperto lower frequencies;

FIGS. 26–30 show alternate sweep down cyclical patterns for applying apower-up sweep pattern in accord with the invention;

FIG. 31 schematically illustrates ultrasound generator circuitry forproviding dual sweeping power-up sweep and variable degas periods, inaccord with the invention;

FIGS. 32 and 33 show multi-frequency ultrasound systems constructedaccording to the invention;

FIG. 34 illustrates a process control system and ultrasound probeconstructed according to the invention;

FIGS. 35 and 36 illustrate two process tanks operating with equal inputpowers but having different cavitation implosion activity;

FIG. 37 illustrates a process probe constructed according to theinvention and for monitoring process characteristics within a processchemistry such as within an ultrasound tank;

FIG. 38 shows a schematic view of a system incorporating the probe ofFIG. 37 and further illustrating active feedback control of energyapplied to an ultrasound tank, in accord with the invention;

FIGS. 39–41 illustrate alternative embodiments of ultrasonic generatorswith universal voltage input, in accord with the invention;

FIG. 42 graphically illustrates an AM burst pattern in accord with theinvention; and FIG. 43 illustrates one burst of primary frequencyultrasound within one of the non-zero AM periods;

FIG. 44 illustrates an AM sweep pattern, in accord with the invention;

FIGS. 45A–45C schematically show one AM power up-sweep generator circuitconstructed according to the invention;

FIG. 46 shows a prior art laminar tank;

FIG. 47 shows an improved laminar tank, constructed according to theinvention;

FIG. 48 shows a quick dump rinse (QDR) tank constructed according to theinvention;

FIG. 49 shows an improved high frequency transducer constructedaccording to the invention;

FIG. 50 illustrates, in a side exploded view, a double compressiontransducer constructed according to the invention;

FIG. 51 shows a prior art transducer with a bias bolt threaded into theupper part of the front driver;

FIG. 52 shows an improved transducer, constructed according to theinvention; with a bias bolt threaded into a lower part of the frontplate;

FIG. 53 illustrates one transducer of the invention utilizing a steelthreaded insert to reduce stress on the front driver;

FIG. 54 shows a side view of a printed circuit board coupled withtransducers as a single unit, in accord with the invention; and FIG. 55shows a top view of the unit of FIG. 54;

FIG. 56 shows an acid-resistant transducer constructed according to theinvention;

FIG. 57 schematically shows one power up-sweep generator circuit of theinvention;

FIG. 58 illustrates a wiring schematic that couples a common voltagesupply to one generator of a system that includes multiple generators,in accord with the invention; FIG. 59 shows a wiring schematic to couplethe generators to a single processing tank with transducers; and FIG. 60schematically shows a circuit coupled to the rotary switch of FIG. 58;

FIG. 61 shows a multi-generator system constructed according to theinvention.

FIG. 62 shows a waveform of a sweeping frequency signal according to theinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 show schematic side and top views, respectively, of anultrasound processing system 10 constructed according to the invention.An ultrasonic generator 12 electrically connects, via electrical paths14 a, 14 b, to an ultrasound transducer 16 to drive the transducer 16 atultrasound frequencies above about 18 khz, and usually below 4 MHz.Though not required, the transducer 16 is shown in FIG. 1 as an array oftransducer elements 18. Typically, such elements 18 are made fromceramic, piezoelectric, or magnetostrictive materials which expand andcontract with applied voltages or current to create ultrasound. Thetransducer 16 is mounted to the bottom, to the sides, or within theultrasound treatment tank 20 through conventional methods, such as knownto those skilled in the art. A liquid (“process chemistry”) 22 fills thetank to a level sufficient to cover the delicate part 24 to be processedand/or cleaned. In operation, the generator 12 drives the transducer 16to create acoustic energy 26 that couples into the liquid 22.

Although the transducer 16 of FIGS. 1 and 2 is shown mounted inside thetank 20, those skilled in the art will appreciate that other mountingconfigurations are possible and envisioned. For example, an alternativeconfiguration is to mount the transducer 16 to an outside surface of thetank 20, typically at the bottom 20 a of the tank 20. The transducerelements 18 of the transducer 16 are of conventional design, and arepreferably “clamped” so as to compress the piezoelectric transducermaterial.

FIG. 3 illustrates a two transducer system 30. Transducer 32 a, 32 b aresimilar to one of the elements 18, FIG. 1. Transducer 32 a includes twoceramic sandwiched elements 34, a steel back plate 38 a, and a frontdrive plate 36 a that is mounted to the tank 20′. Transducer 32 bincludes two ceramic sandwiched elements 34, a steel back plate 38 b,and a front drive plate 36 b that is mounted to the tank 20′. Bolts 39a, 39 b pass through the plates 38 a, 38 b and screw into the driveplates 36 a, 36 b, respectively, to compresses the ceramics 34. Thetransducers 32 are illustratively shown mounted to a tank surface 20′.

The transducers 32 a, 32 b are driven by a common generator such asgenerator 12 of FIG. 1. Alternatively, multiple generators can be used.The ceramics 34 are oriented with positive “+” orientations together orminus “−” orientations together to obtain cooperative expansion andcontraction within each transducer 32. Lead-outs 42 illustrate theelectrical connections which connect between the generator and thetransducers 32 so as to apply a differential voltage there-across. Thebolts 39 a, 39 b provide a conduction path between the bottoms 43 andtops 45 of the transducers 32 to connect the similar electrodes (hereshown as “−” and “−”) of the elements 34.

The length 40 a, 40 b of transducers 32 a, 32 b, respectively, determinethe transducer's fundamental resonant frequency. For purposes ofillustration, transducer 32 a has a fundamental frequency of 40 khz, andtransducer 32 b has a fundamental frequency of 44 khz. Transducers 32 a,32 b each have a finite ultrasound bandwidth which can be adjusted,slightly, by those skilled in the art. Typically, however, thebandwidths are about 4 khz. By choosing the correct fundamentalfrequencies, therefore, an overlap between the bandwidths of the twotransducers 32 a, 32 b can occur, thereby adding additional range withinwhich to apply ultrasound 26 a′, 26 b′ to liquid 22′.

The acoustic energy 26′ applied to the liquid 22′ by the combination oftransducers 32 a, 32 b is illustrated graphically in FIG. 4. In FIG. 4,the “x” axis represents frequency, and the “y” axis representsacoustical power. The outline 44 represents the bandwidth of transducer32 a, and outline 46 represents the bandwidth of transducer 32 b.Together, they produce a combined bandwidth 43 which produces arelatively flat acoustical energy profile to the liquid 22′, such asillustrated by profile 48. The flatness of the acoustic profile 48within the bandwidth 43 is preferably within a factor of two of anyother acoustic strength within the bandwidth 43. That is, if the FWHM(full width, half maximum) defines the bandwidth 43; the non-uniformityin the profile 48 across the bandwidth 43 is typically better than thisamount. In certain cases, the profile 48 between the two bandwidths 44and 46 is substantially flat, such as illustrated in FIG. 4.

The generator connected to lead-outs 42 drives the transducers 32 a, 32b at frequencies within the bandwidth 43 to obtain broadband acousticaldisturbances within the liquid 22′. As described herein, the manner inwhich these frequencies are varied to obtain the overall disturbance isimportant. Most preferably, the generator sweeps the frequencies throughthe overall bandwidth, and at the same time sweeps the rate at whichthose frequencies are changed. That is, one preferred generator of theinvention has a “sweep rate” that sweeps through the frequencies withinthe bandwidth 43; and that sweep rate is itself varied as a function oftime (a phenomenon denoted herein as “sweep the sweep rate”). Inalternative embodiments of the invention, the sweep rate is variedlinearly, randomly, and as some other function of time to optimize theprocess conditions within the tank 20′.

With further reference to FIGS. 1 and 2, each of the elements 18 canhave a representative bandwidth such as illustrated in FIG. 4.Accordingly, an even larger bandwidth 43 can be created with three ormore transducers such as illustrated by transducers 32 a, 32 b. Inparticular, any number of combined transducers can be used. Preferably,the bandwidths of all the combined transducers overlap-to provide anintegrated bandwidth such as profile 48 of FIG. 4. As such, eachtransducer making up the combined bandwidth should have a uniqueresonant frequency.

Those skilled in the art understand that each of the transducers 18 and32 a, 32 b, FIGS. 1 and 3, respectively, have harmonic frequencies whichoccur at higher mechanical resonances of a primary resonant frequency.It is one preferred embodiment of the invention that such transducersoperate at one of these harmonics, i.e., typically the first, second,third or fourth harmonic, so as to function in the frequency range of100 khz to 350 khz (see, e.g., FIG. 5, which illustrates an appliedultrasonic bandwidth of 102 khz to 110 khz in a manner similar as inFIG. 4). This frequency range provides a more favorable environment foracoustic processes within the liquid 22, 22′ as compared to lowfrequency disturbances less than 100 khz. For example, ultrasoundfrequencies around the 40 khz frequency can easily cause cavitationdamage in the part 24. Further, such frequencies tend to create standingwaves and other hot spots of spatial cavitation within the liquid.

FIGS. 6–10 illustrate alternative backplate configurations according tothe invention. Unlike the configuration of FIG. 3, the backplates ofFIGS. 6–10 are shaped to flatten or modify the power output from theentire transducer when driven over a range of frequencies such as shownin FIG. 4. Specifically, FIG. 6 includes a backplate 58 that, forexample, replaces the backplate 38 of FIG. 3. A portion of the bolt 39is also shown. As illustrated, the backplate 58 has a cut-away section60 that changes the overall acoustic resonance of the transducer overfrequency. Similarly, the backplate 58 a of FIG. 7 has a curved section60 a that also changes the overall acoustic resonance of the transducerover frequency. FIGS. 8, 9 and 10 similarly have other sloped or curvedsections 60 b, 60 c, and 60 d, within backplates 58 b, 58 c and 58 d,respectively, that also change the overall acoustic resonance of thetransducer.

The exact configuration of the backplate depends upon the processingneeds of the ultrasound being delivered to a tank. For example, it istypically desirable to have a flat or constant power over frequency,such as shown in FIG. 4. Accordingly, for example, the backplate and/orfront driver can be cut or shaped so as to help maintain a constantpower output such that the energy generated by the transducer at anygiven frequency is relatively flat over that bandwidth. Alternatively,the backplate can be cut or shaped so as to provide a varying poweroutput, over frequency, such as to compensate for other non-linearitieswithin a given ultrasound system.

FIG. 17 illustratively shows how standing waves are formed within onetransducer 69 of the invention over various frequencies 61, 62, 63.Because of the shaped surface 70 of the backplate 59, there are nopreferred resonant frequencies of the transducer 69 as standing wavescan form relative to various transverse dimensions of the transducer 69.By way of example, frequency 62 can represent 38 khz and frequency 63can represent 42 khz.

FIG. 11 illustrates still another transducer 80 of the invention thatprovides for changing the power output as a function of frequency. Thefront driver 82 and the backplate 84 are connected together by a bolt 86that, in combination with the driver 82 and backplate 84, compress theceramics 88 a, 88 b. The configuration of FIG. 11 saves cost since thefront driver 82 has a form fit aperture-sink 90 (the bolt head 86 awithin the sink 90 are shown in a top view in FIG. 12) that accommodatesthe bolt head 86 a. A nut 86 b is then screwed onto the other end of thebolt 86 and adjacent to the backplate 84 such that a user can easilyaccess and remove separate elements of the transducer 80.

The front driver 82 and/or backplate 84 (the “backplate” also known as“back mass” herein) are preferably made from steel. The front driver 82is however often made from aluminum. Other materials for the frontdriver 82 and/or the backplate 84 can be used to acquire desiredperformance characteristics and/or transducer integrity.

FIG. 13 shows another transducer 92 that includes a backplate 94 and afront driver 96. A bolt 98 clamps two ceramic elements 97 a, 97 btogether and between the backplate 94 and driver 96; and that bolt 98has a bolt head 100 that is approximately the same size as the diameter“D” of the transducer 92. The bolt head 100 assists the overalloperation of the transducer 92 since there is no composite interface ofthe bolt 98 and the driver 96 connected to the tank. That is, the bondbetween the tank and the transducer 92 is made entirely with the bolthead 100. By way of comparison, the bond between the tank and thetransducer 80, FIG. 11, occurs between both the bolt 86 and the driver82. A sloped region 99 provides for varying the power output overfrequency such as described herein.

FIG. 14 illustrates one end 102 of a transducer of the invention that issimilar to FIG. 13 except that there is no slope region 99; andtherefore there is little or no modification of the power output fromthe transducer (at least from the transducer end 102).

FIGS. 15 and 16 show further transducer embodiments of the invention.FIG. 15 shows a transducer 110 that includes a driver 112, backplate114, bolt 116, ceramic elements 118 a, 118 b, and electrical lead-outs120. The backplate is shaped so as to modify the transducer power outputas a function of frequency. The driver 112 is preferably made fromaluminum.

FIG. 16 illustrates an alternative transducer 120 that includes abackplate 122, driver 124, bolt 126, ceramic elements 128 a, 128 b, andlead outs 130. One or both of the backplate and driver 122, 124 are madefrom steel. However, the front driver 124 is preferably made fromaluminum. The bolt head 126 a is fixed within the driver 124; and a nut126 b is screwed onto the bolt 126 to reside within a cut-out 122 a ofthe backplate 122. The backplate 122 and front driver 129 are sealed atthe displacement node by an O-ring 123 to protect the electricalsections (i.e., the piezoelectric ceramics and electrodes) of thetransducer 120 under adverse environmental conditions.

The designs of FIGS. 13–14 have advantages over prior art transducers inthat the front plate in each design is substantially flush with the tankwhen mounted to the tank. That is, the front plates have a substantiallycontinuous front face (e.g., the face 112 a of FIG. 15) that mountsfirmly with the tank surface. Accordingly, such designs support the tanksurface, without gap, to reduce the chance of creating cavitationimplosions that might otherwise eat away the tank surface and createunwanted contaminants.

FIG. 18 shows one preferred arrangement (in a bottom view) for mountingmultiple transducers 140 to the bottom 142 a of a process tank 142.Specifically, the lateral spacing between transducers 140—each with adiameter X—is set to 2X to reduce the cavitation implosions around thetransduces 140 (which might erode the generally expensive tank surface142 a). By way of example, if the transducer 140 has a two inch diameter(i.e., X=2″), then the spacing between adjacent transducers 140 is fourinches. Other sizes can of course be used and scaled to user needs andrequirements. FIG. 9(d) illustrates, in a cross sectional schematicview, a standing wave 144 that is preferentially created betweenadjacent transducers 140′ with diameters X and a center to centerspacing of 2X. The standing wave 144 tends to reduce cavitation anderosion of the tank 142′ surface.

Surface cavitation is intense cavitation that occurs at the interfacebetween the solution within the tank and the radiating surface uponwhich the ultrasonic transducers are mounted. There are several problemsassociated with surface cavitation damage. First, it is often intenseenough to erode the material of the radiating surface. This caneventually create a hole in the radiation surface, destroying the tankThe erosion is also undesirable because it introduces foreign materialsinto the cleaning solution. Surface cavitation further generatescavitation implosions with higher energy in each cavitation implosionthan exists in the cavitation implosions in the process chemistry. Ifthe cavitation implosions in the process chemistry are at the properenergy level, than there is the possibility that the higher energycavitation implosions at the surface cavitation will cause pitting orcraters in the parts under process. In addition, the energy that goesinto creating the surface cavitation is wasted energy that is betterused in creating bulk cavitation.

FIG. 20 illustrates a closed hex spacing pattern 149 of transducerelements 150 that causes the radiating membrane 151 (i.e., the surfaceof the tank to which the elements are bonded to) to vibrate in asinusoidal pattern such that surface cavitation is prevented or reduced.In a side view, FIG. 21 illustrates a G-10 isolator 153 bonded betweentwo of the transducers 150′ (and specifically the front driver 150 a)and the radiating surface 151′, i.e., the wall of the tank 154 holdingthe process chemistry 156. The G-10 153 operates to further reduceunwanted surface cavitation, often times even when the closed hexspacing pattern of FIG. 20 is not possible. Piezoelectric elements 155are sandwiched between the front plate 150 a and backplate 154. FIG. 22shows an exploded side view of one of the G-10 mounted transducer 150″of FIG. 21. Layers of epoxy 160 preferably separate the G-10 isolator153 from the transducer 150″ and from the surface 152′.

Most ultrasonic processes, including cleaning, have two distinct stages.The first stage is usually preparation of the liquid and the secondstage is the actual process. The system 200 of FIGS. 23–25 reduces thetime for liquid preparation and accomplishes the task to a degree whereshorter process times are possible.

The invention of FIG. 23 utilizes the sound fields as an upward drivingforce to quickly move contaminants to the surface 207 a of the liquid207. This phenomenon is referred to herein as “power up-sweep” andgenerally cleans the liquid more quickly and thoroughly so that partprocessing can be done with less residual contamination.

More particularly, FIG. 23 shows a system 200 constructed according tothe invention. A generator 202 drives a plurality of transducers 204connected to a process tank 206, which holds a process chemistry 207.The generator 202 drives the transducers 204 from an upper frequency(f_(upper)) to a lower frequency (f_(lower)), a shown in FIG. 25. Oncef_(lower) is reached, a frequency control subsystem 208 controls thegenerator 202 so as to drive the transducers 204 again from f_(upper) tof_(lower) and without driving the transducers from f_(lower) tof_(upper). In this manner, only decreasing frequencies are imparted tothe process chemistry 207; and acoustic energy 210 migrates upwards(along direction 217), pushing contamination 211 upwards and out of thetank 206.

As shown in FIG. 24, the two stage ultrasonic processing system 200 canalternatively cycle the transducers 204 from f_(upper) to f_(lower)every other half cycle, with a degas, quiet or off half cycle 222between each power burst. The control subsystem 208 of this embodimentthus includes means for inhibiting the flow of energy into the tank 206over a second half cycle so that the quiet period 222 is realized. It isnot necessary that the time periods of the first and second one-halfcycles 222 a, 222 b, respectively, be equal.

FIGS. 24 and 25 also show that the rate at which the frequencies areswept from f_(upper) to f_(lower) can vary, as shown by the shorter orlonger periods and slope of the power bursts, defined by the frequencyfunction 220.

The generator 202 preferably produces frequencies throughout thebandwidth of the transducers 204. The generator 202 is thus preferably asweep frequency generator (described in U.S. Pat. Nos. 4,736,130 and4,743,789) or a dual sweep generator (described in International PatentApplication PCT/US97/12853) that will linearly or non-linearly changefrequency from the lowest frequency in the bandwidth to the highestfrequency in the bandwidth; and that will thereafter reverse directionand sweep down in frequency through the bandwidth. The invention of FIG.25 has an initial stage where the sweeping frequency only moves from thehighest bandwidth frequency to the lowest bandwidth frequency. Once thelowest frequency is reached, the next half cycle is the highestfrequency and the sweep starts again toward the lowest frequency. Analternative (FIG. 24) is to shut the ultrasonics off when the lowestfrequency is reached and reset the sweep to the highest frequency. Afteran ultrasonics quiet period 222, another sweep cycle from high frequencyto low frequency occurs. This. “off” period followed by one directionalsweep is repeated until contamination removal is complete; and then theprocessing can start in a normal way. Alternatively, a power up-sweepmode can be utilized for improved contamination removal duringprocessing.

The reason that contamination is forced to the surface 207 a of theprocess chemistry 207 in the system of FIG. 23 is because the nodalregions move upward as frequency is swept downward. Contaminationtrapped in nodal regions are forced upward toward the surface as nodesmove upward. Generally, the system of FIG. 23 incorporates a type offrequency modulation (FM) where frequency changes are monotonic fromhigher to lower frequencies. Transducers 204 mounted to the bottom ofthe process tank 206 generate an ever expanding acoustic wavelength inthe upward direction 217 (i.e., toward the surface 207 a of the processchemistry 207). This produces an acoustic force 210 which pushescontamination 211 to the surface 207 a where the contamination 211overflows the weirs 213 for removal from the tank 206.

Those skilled in the art should appreciate that methods and systemsexist for sweeping the applied ultrasound energy through a range offrequencies so as to reduce resonances which might adversely affectparts within the process chemistry. See, e.g., U.S. Pat. Nos. 4,736,130and 4,743,789 by the inventor hereof and incorporated by reference. Itis further known in ultrasonic generators to “sweep the sweep rate” sothat the sweep frequency rate is changed (intermittently, randomly, witha ramp function, or by another function) to reduce other resonanceswhich might occur at the sweep rate. By way of example, the inventor ofthis application describes such systems and methods in connection withFIGS. 3, 4, 5A, 5B, 12A, 12B and 12C of International Application No.PCT/US97/12853, which is herein incorporated by reference.

The variable slope of the frequency function 220 of FIGS. 24 and 25illustrates that the time period between successive power up sweeps,from f_(upper) to f_(lower), preferably changes so as to “sweep thesweep rate” of the power up sweep. Accordingly, the power up-sweeppreferably has a non-constant sweep rate. There are several ways toproduce a non-constant power up-sweep rate, including:

(a) As illustrated in FIG. 28, sweep down in frequency (i.e., fromf_(upper) to f_(lower)) at a relatively slow rate, typically in therange of 1 Hz to 1.2 khz, and sweep up in frequency (i.e., fromf_(lower) to f_(upper)) during the recovery time at a rate about tentimes higher than the sweep down frequency rate. Vary the rate for eachcycle. This cycle is repeated during processing.

(b) As illustrated in FIG. 29, sweep down in frequency at a relativelyslow rate and shut the generator 202 off (such as through the controlsubsystem 208) at periods 225′ when the lowest frequency f_(lower) inthe bandwidth (bandwidth=f_(upper)−f_(lower)) is reached. During the offtime 225′, a degassing period 222 can occur as in FIG. 24 due tobuoyancy of the gas bubbles; and the subsystem 208 resets the generator202 to the highest frequency for another relatively slow rate ofsweeping from f_(upper) to f_(lower), each time reducing contaminants.Vary the time of the degas period. Repeat this cycle during processing.

(c) As a function of time, change or “sweep” the power up-sweep rate atoptimum values (1 Hz to 1.2 khz) of the rate, as shown in FIG. 28. Thechange in the upward sweep rate and the change in the downward sweeprate can be synchronized or they can be random with respect to oneanother.

(d) For the case where there is a degas period, as in FIGS. 24 and 29(i.e. the recovery period when the generator is off or unconnected whileresetting from low frequency to high frequency), vary the length of thedegas period 222 (FIG. 24), 225′ (FIG. 29) randomly or as a function oftime such as through a linear sweep rate time function. This techniquehas an advantage for cases where there is one optimum power up-sweeprate (i.e., the rate of frequency change between f_(upper) andf_(lower)) and, accordingly, low frequency resonances are eliminated bychanging the overall rate. In such a technique, the slope of thefrequency function 220′ in FIG. 29, is constant, though the period ofeach degas period 225′ changes according to some predefined function.

(e) As shown in FIG. 30, sweep the rate with a combination of (c) and(d) techniques above.

Note that in each of FIGS. 24–30, the x axis represents time (t) and they axis represents frequency f.

FIG. 31 shows a schematic 250 illustrating the most general form ofgenerator circuitry providing both non-constant power up-sweep rate andnon-constant degas period, as described above.

Extraction Tool Analysis

When evaluating one ultrasonic cleaner versus another as to itsusefulness as an extraction tool, the slope between the first two pointsand the magnitude of the initial point are meaningful if the parts beingextracted start out with identical contamination. If not, the resultscan be misleading. For example, consider two cleaners (e.g., tanks) thateach remove 90% of the contamination on each trial. If cleaner A istested with a part starting with 10,000 particles of contamination,point #1 will be 9,000 and point #2 will be 900. The slope is 8,100. Nowif cleaner B is tested with a part starting with 1,000 particles, point#1 will be 900 and point #2 will be 90. Cleaner B thus has a slope of810, which is ten times less than for cleaner A in removing the samepercentage of contamination per run.

A preferred technique of the invention is to measure the slopes when thepoints are plotted on semi-log paper or to calculate log (count #1)−log(count #2) and compare figures between tanks. Since log (count #1)−log(count #2) equals log (count #1/count #2), a similar result is obtainedif you compare the quotient of count #1 divided by count #2 for eachcleaner.

The magnitude of the initial point does not provide significantinformation. However, the semi-log slope permits determining initialcontamination count as long as the extraction time for each trial isshort enough so the first three points are in a straight line. This lineis extended back to the y-axis where x=0 to get the initialcontamination count.

To evaluate two extraction tools, experimentation leads to a trail timethat provides three points with each tool on a straight line whenplotted on semi-log paper. For each tool, E for extraction is thencalculated as log (count #1)−log (count #2). The tool with the largest Eis the best

The procedure for evaluating part cleanliness may be different than forevaluating tools, such that the magnitude of point #1 is nowsignificant. However, the technique can be similar: choose a trial timeto give three points in a straight line on semi-log paper; extrapolateback to the y-axis to get the initial number of particles on the part;continue trials until the count levels off or becomes zero (minusinfinity on a semi-log plot); if the count became zero, there is noerosion, therefore, add together all the particles removed and subtractthis from the extrapolated initial number of particles, indicating theremaining contamination count on the part; if the count leveled off toan erosion level, calculate the remaining contamination on the part bythe formula:

$C = {\left( {y\text{-}{axis}_{intercept}} \right) - {\sum\limits_{i = 1}^{n}{trialcount}_{i}} + {nx}}$where x=the erosion count per trial and n=the number of trials

The above analysis now provides the amount of contamination initially onthe part (y-axis intercept), the contamination generated by erosion(nx), and the remaining contamination (C) on the part after all theextractions.

The energy in each cavitation implosion is the single most importantcharacteristic of a high intensity ultrasonic field in a liquid used forcleaning or processing delicate parts. This energy value changes withchemistry characteristics, liquid temperature, and pressure andfrequency of the ultrasound. Setting the center frequency of theultrasonic generator to specific values over a wide range is the mostpractical way to choose the appropriate energy in each cavitationimplosion for a given process. The invention of FIG. 32 provides thisfunction with a single generator.

Specifically, FIG. 32 shows a system 300 including a generator 302 andtransducers 304 that can be switched, for example, to either 72 khz or104 khz operation. The transducers 304 operate to inject sonic energy305 to the process chemistry 307 within the tank 306. Because of theimpedance characteristics at these frequencies, the generator 302includes a constant power output circuit 306 that changes the centerfrequency output from the generator 302 while maintaining constantoutput power. The circuit 306 includes a switch section 308 thatswitches the output frequency from one frequency to the next with nointermediate frequencies generated at the output (i.e., to thetransducers 304).

A similar system 310 is shown in FIG. 33, where switching betweenfrequencies does not utilize the same power circuit. In FIG. 33, thegenerator 312 includes at least two drive circuits for producingselected frequencies f₁ and f₂ (these circuits are illustratively shownas circuit (f₁), item 314, and circuit (f₂), item 316). Before thereactive components in either of the circuits 314, 316 can be switchedto different values, the output circuit 318 shuts down the generator 312so that stored energy is used up and the relay switching occurs in azero voltage condition.

From the above, one skilled in the art should appreciate that the system310 can be made for more than two frequencies, such as for 40 khz, 72khz and 104 khz. Such a system is advantageous in that a singletransducer (element or array) can be used for each of the multiplefrequencies, where, for example, its fundamental frequency is 40 khz,and its first two harmonics are 72 khz and 104 khz.

An alternative system is described in connection with FIG. 61.

FIG. 34 illustrates a system 400 and process probe 402 constructedaccording to the invention. A generator 404 connects to transducers 406to impart ultrasonic energy 403 to the process chemistry 407 within thetank 408. The probe 402 includes an enclosure 410 that houses a liquid412 that is responsive to ultrasound energy within the liquid 407. Theenclosure 410 is made from a material (e.g., polypropylene) thattransmits the energy 403 therethrough In response to the energy 403,changes in or energy created from liquid 412 are sensed by the analysissubsystem 414. By way of example, the liquid 412 can emit spectralenergy or free radicals, and these characteristics can be measured bythe subsystem 414. Alternatively, the conduit 416 can communicateelectrical energy that indicates the conductivity within the enclosure.This conductivity provides an indication as to the number of cavitationimplosions per unit volume within the process chemistry 407. The conduit416 thus provides a means for monitoring the liquid 412. A thermocouple420 is preferably included within the enclosure 410 and/or on theenclosure 410 (i.e., in contact with the process chemistry 407) so as tomonitor temperature changes within the enclosure 410 and/or within theprocess chemistry 407. Other characteristics within the tank 408 and/orenclosure 410 can be monitored by the subsystem 414 over time so as tocreate time-varying functions that provide other useful informationabout the characteristics of the processes within the tank 408. Forexample, by monitoring the conductivity and temperature over time, theamount of energy in each cavitation explosion may be deduced within theanalysis subsystem 414, which preferably is microprocessor-controlled.

The prior art is familiar with certain meters which measure soundcharacteristics and cavitations within an ultrasonic tank. Each of themeters gives one number, usually in units of watts per gallon, andsometimes in undefined units such as cavities. However, the activity ina cavitating ultrasonic tank is very complex and no single numberadequately describes this activity. For example, as shown in FIGS. 35and 36, it is possible to have two ultrasonic tanks 420, 422, bothhaving the same input power (i.e. watts per gallon) but each having verydifferent ultrasonic activity characteristics. The first tank 420 mighthave relatively few high energy cavitation implosions 420 a while thesecond tank 422 has many low energy cavitation implosions 422 a(specifically, FIGS. 35 and 36 show cavitation implosions 420 a, 422 aduring a fixed time period in the two tanks 420, 422 having equal inputenergies). At least two numbers are thus necessary to describe thissituation: the energy in each cavitation implosion and the cavitationdensity. The energy in each cavitation implosion is defined as the totalenergy released in calories from a single cavitation event; and thecavitation density is defined as the number of cavitation events in onecubic centimeter of volume during a 8.33 millisecond time period. Note,in Europe and other countries with fifty Hz power lines, the cavitationevents in one cubic centimeter are counted over a ten millisecond timeperiod and multiplied by 0.833. This technique provides the mostaccurate measurement for the common ultrasonic systems that have theiramplitude modulation pattern synchronized by two times the power linefrequency.

In most ultrasonic systems, the cavitation density also varies as afunction of time. Accordingly, this is a third characteristic thatshould be measured when measuring ultrasonic activity in a tank.

FIG. 37 thus illustrates one probe 650 of the invention which permitsthe calculation of these important parameters. Specifically, the probe650 measures average conductivity conductivity as a function of time,and change in temperature.

A characteristic of ultrasonic cavitation in aqueous solutions is theproduction of free radicals, ions and super oxides. These by-products ofthe cavitation increase the conductivity of the aqueous solution. Ameasure of the conductivity is thus a function of the number ofcavitation implosions present in the aqueous sample, and the timevariation of this conductivity is a measure of how the cavitationdensity varies as a function of time.

Another characteristic of cavitation is that it heats the aqueoussolution. This is because all the energy released during each cavitationimplosion becomes heat energy. By measuring the change in temperature ofthe aqueous sample, therefore, and by knowing its mass and specificheat, one can calculate the total energy released from the cavitation bythe following formula: energy (calories) equals specific heat (no units,i.e., a ratio) times mass (grams) times the change in temperature (°C.). When the amount of energy released is known, as well as the numberof cavitation implosions that released this energy, a division of thequantities gives the energy in each cavitation implosion.

The probe 650 is similar in operation to the probe 402 of FIG. 34 andincludes a fixed sample volume of aqueous solution 652 (or otherchemistry that changes conductivity in an ultrasonic field) contained inthe probe tip 650 a. The probe tip 650 a is designed to cause minimaldisturbance to the ultrasonic field (e.g., the field 403 of FIG. 34).Accordingly, the probe tip 650 a is preferably made of a material thathas nearly the same acoustic impedance as the liquid being measured andthat has low thermoconductivity. Polypropylene works well since it andwater have nearly the same acoustic impedance.

The probe 650 thus includes, within the probe tip 650 a, two electrodes654, 656 to measure conductivity, and a temperature measuring probe(e.g., a thermocouple) 658 to monitor the temperature of the fixed massof aqueous solution 652. These transducers 654, 656 and 658 areconnected to data wires for sampling of the transducer responses. A datacollection instrument (e.g., an A/D sensor interface board and acomputer) connects to the wires 670 out of the probe 650 to measuretemperature rise as a function of time, ΔT=g(t), and to evaluate thisquantity over a specific time period t′, in seconds, i.e., ΔT=g(t′). Thedata collection instrument also measures the initial conductivity, C₀,without ultrasonics, and the conductivity as a function of time, C=h(t),within the ultrasonic field. Fixed constants associated with the probeshould also be stored, including the specific heat (p) of the liquid652, the volume (V) of the liquid 652 (in cubic centimeters), the mass(m) of the liquid 652 (in grams), and the functional relationshipn=f(C,C₀) between conductivity and the number of cavitation implosionsoccurring in the probe tip 650 a in 8.33 milliseconds determined bycounting the sonoluminescence emissions over a 8.33 millisecond periodand plotting this versus the conductivity measurement. The instrumentthen calculates the ultrasonic parameters from this informationaccording to the following formulas:

(a) cavitation density=D=n/V=f(C,C₀)/V

(b) energy in each cavitationimplosion=E=(0.00833)(p)(m)(g(t′))/V/f(C,C₀)/t′

(c) cavitation density as a function of time=f(h(t))/V

These three measured parameters are then fed back to the generator tocontinuously control the output of the generator to optimum conditions.FIG. 38 shows a complete system 675 for monitoring and processing datafrom such a probe 650′ and for modifying applied ultrasound energy 676applied to the process chemistry 678. Specifically, the system 675monitors the parameters discussed above and, in real time, controls thegenerator 680 to adjust its output drive signals to the transducers 682at the tank 684. The data collection instrument 685 connects to thewiring 670′ which couples directly to the transducers within the probetip 650′. The instrument 685 generates three output signal linescorresponding to measured parameters: the “A” signal line corresponds tothe energy in each cavitation implosion, the “B” signal line correspondsto the cavitation density output, and the “C” signal line corresponds tothe cavitation density as a function of time. These signal lines A–C areinput to separate comparators 686 a, 686 b and 686 c. The comparators686 a–c are coupled to signal lines D–F, respectively, so that the inputsignal lines A–C are compared to user selected optimum values for eachof the parameters. Typically, the user employs empirical experimentationto arrive at the optimum values for a particular tank 684 and chemistry678. The results from the comparators 686 are input to the controlsystem 690, which controls the generator 680 (those skilled in the artshould appreciate that the controller 690 and generator 680 can be, andpreferably are, coupled as a single unit).

The energy in each cavitation implosion decreases as the frequency ofthe ultrasonics 676 increases and as the temperature of the solution 678increases. The energy in each cavitation implosion is measured andcompared to the optimum value (set by signal lines D–F) for the process,and if the measured value has a higher energy value than the optimumvalue, as determined by the comparators 686, the center frequency of thegenerator 680 is increased (by the controller 690 receiving data at the“center frequency input control”) until the values are equal. If thereis not enough range in the center frequency adjustment to reach theoptimum value, then the temperature of the solution 678 is increased bythe control system 690 until the optimum value is reached. Analternative is to utilize a switchable frequency generator, as describedabove, so as to change the drive frequency to one where the energy ineach cavitation implosion is not greater than the optimum value, andwithout changing the solution temperature.

The cavitation density increases as the ultrasonic power into the tank684 increases. Therefore, the cavitation density measurement fed back tothe generator 680 is compared against the optimum value of cavitationdensity for the process; and if the measured value is lower than theoptimum value, the generator output power is increased (by thecontroller 690 receiving data at the “power control”) until the twovalues are equal. If the measured value is greater than the optimumvalue, the generator output power is decreased until the values areequal.

Cavitation density as a function of time is controlled by the amplitudemodulation (AM) pattern of the generator output 692. Therefore themeasured cavitation density as a function of time is measured and thegenerator's AM pattern is adjusted (via the controller 690 receivingdata at the “AM Control”) until the measured function equals the optimumfunction.

FIG. 39–41 illustrate separate embodiments of universal voltage inputultrasonic generators, in accord with the invention. These embodimentsare made to solve the present day problems associated with separatedesigns made for countries with differing power requirements (in voltsA-C, or “VAC”), such as:

100 VAC Japan, and intermittently during brown-outs in the U.S. 120 VACU.S. 200 VAC Japan 208 VAC U.S. 220 VAC Most of Europe exceptScandinavia and U.K. 240 VAC U.S., U.K., Norway, Sweden and Denmark “Z”VAC Corresponding to unusual voltages found in France and other worldlocations

These voltages are obviously problematic for industry suppliers ofultrasonic generators, who must supply the world markets. The inventionof FIGS. 39–41 eliminates the chance that a particular world consumerreceives an incorrect generator by providing universal voltagegenerators that operate, for example, between 86 VAC and 264 VAC.

In FIG. 39, an ultrasonic generator 500 is shown connected to a 300 VDCsource 501. A power factor correction (PFC) circuit 502 connects to thefront end of the generator 500 to produce a regulated 300 VDC. Aswitching regulator 504 regulates the 300 VDC to +12V and +15V. Thegenerator 500 can be represented, for example, as the circuit of FIG.31, except that the “high voltage supply” is replaced by the PFC circuit502 and the +12V and +15V are replaced with control voltages from theregulator 504.

FIG. 40 illustrates a generator 510 connected to a universal inputswitching regulator 512. The regulator 512 generates a set 513 of DCvoltages for the generator 510. The generator 510 includes circuitry 514that operates with the set 513. The generator 510 can be represented,for example, as the circuit of FIG. 31, except that the “high voltagesupply” and the +12V and +15V are replaced with output voltages from theregulator 512.

Those skilled in the art should appreciate that methods and systemsexist for utilizing the power line to acquire amplitude control forultrasonic generators. By way of example, the inventor of thisapplication describes such systems and methods in connection with FIGS.3, 4, 5A, 5B and 7 of International Application No. PCT/US97/12853.Specifically, an amplitude control subsystem is achieved by rectifyingthe AC power line and selecting a portion of the rectified line voltagethat ends at the desired amplitude (such as between zero and 90° orbetween 180° and 270° of the signal). In this manner, amplitudemodulation is selectable in a controlled manner as applied to the signaldriving the transducers from the generator. For example, by selectingthe maximum amplitude of 90° in the first quarter sinusoid, and 270° inthe third quarter sinusoid, a maximum amplitude signal is provided.Similarly, a one-half amplitude signal is generated by choosing the 30°and 210° locations of the same sinusoids. By way of a further example, aone-third amplitude signal is generated by choosing 19.5° and 199.5°,respectively, of the same sinusoids.

FIG. 41 illustrates a generator 530 which operates at a DC voltage lessthan or equal to (86)(√{square root over ( )}2) volts. As in amplitudecontrol, a triac 532 is used to select that portion of the power linevoltage with an amplitude equal to the generator DC voltagerequirements. The signal 534 is rectified and filtered by the bridgerectifier and filter 536 to obtain the constant DC voltage 538 in therange less than or equal to (86)(√{square root over ( )}2) volts. Thegenerator 530 can be represented, for example, as the circuit of FIG.31, except that the “high voltage supply” is replaced by the voltagefrom the bridge rectifier and filter 536 and the +12V and +15V arereplaced with output voltages from the regulator 540, as above.

In another embodiment, the selected AC voltage angle can be reduced tolower the DC voltage to reduce the amplitude of the ultrasonic drivesignal.

The “power up sweep” features of the invention also apply to amplitudemodulation, where an AM pattern of the AM frequency varies according tothe power up-sweep techniques discussed above, and preferably at thesame time with the techniques of “sweep the sweep rate”, as discussedherein. With power up-sweep AM, the AM pattern modulation creates anadditional upward force on contamination while eliminating low frequencyresonances.

FIG. 42 illustrates an AM (amplitude modulation) pattern 600 of theinvention, where the frequency of the AM is constantly decreasing withincreasing time t More particularly, ultrasonic bursts of energy (asshown in FIG. 43, with a frequency f) are contained within each of thenon-zero portions 600 a of the pattern 600. As time increases, longerand longer bursts of energy are applied to the associated transducers.In the optimum case, the ultrasound frequency within each burst of FIG.43 varies with a power up sweep, from f_(upper) to f_(lower), asdiscussed above.

FIG. 44 shows a plot 610 of AM frequency verses time t. As shown, the AMfrequency monotonicly changes from a high frequency, f_(high), to a lowfrequency, f_(low). When f_(low) is reached, a degas or quiet period 612is typically introduced before the cycle 614 repeats.

Note that the sweep rate of the change of the AM frequency along theslope 616 can and preferably does change at a non constant sweep rate.The rate of AM frequency change can thus be non-constant. The degasperiod 612 can also be non constant. The degas period 612 can also besubstantially “0”, so that no time is permitted for degas.

Generally, there are three ways to change the AM frequency. The burstlength “L” (FIG. 43) can be changed, the time between bursts can bechanged (e.g., the periods 600 b, FIG. 42, where the amplitude is zero);or both parameters can be changed simultaneously.

FIGS. 45A–45C schematically illustrate electronics for one ultrasonicgenerator with AM power up-sweep capability, in accord with theinvention.

FIG. 46 illustrates a prior art laminar tank 700. Contamination withinthe tank 700 is a problem in critical cleaning operations because thecontamination can redeposit on the part 701 under process. A common wayto remove contamination from the cleaning solution 702 of the tank 700is to build the tank 700 with overflow weirs 704 and to constantly addpure solution, or recirculate filtered solution, into the bottom of thetank at a solution inlet 706. The solution injected through the inlet706 travels through the tank volume and out over the overflow weirs 704.Solution which overflows the weirs 704 exits through outlets 705 fordisposal or filtering.

The problem with cleaning the solution 702 in this manner is that thecleaning time is excessive because there is mixing of pure or filteredsolution with contaminated solution while solution passes through thevolume of the tank 700. The mixing causes a dilution of the contaminatedsolution by the pure or filtered solution. The result is that dilutedsolution overflows the weirs 704; and the contamination within the tank700 is eliminated logarithmically rather than linearly. Logarithmicelimination theoretically takes an infinite amount of time to reachzero, whereas linear elimination has a theoretical finite time when thetank becomes contamination free.

The tank 720 of FIG. 47, constructed according to the invention, thusincludes features which significantly reduce the afore-mentionedproblems. Specifically, the tank 720 operates such that the solution702′ in the tank 720 moves in a piston like fashion from the bottom 720a to the top 700 b of the tank 700, resulting in little or no mixing ofcontaminated solution with the new or filtered solution. Near linearremoval of the contamination within the tank 700 results, providing forrapid clean up.

The tank 720 has a number of baffles that: reduce the velocity of theclean solution; equalize the pressure of the clean solution; andintroduce the solution into the tank 720 with even distribution at thebottom 720 a of the tank 720. The first baffle 722 reduces the velocityof the solution injected through the inlet 706′. The second baffle 724evenly distributes the solution at the bottom of the tank 720 a. Baffle724 has a plate 726 with a large number of small holes 728 cuttherethrough to give a minimum of 45% open area so that the pressureacross any hole is minimized.

The combination of the baffles 722 and 724 operate to provide smoothmovement of contaminated solution upwards and over the wirers 704′. Thetank 720 thus augments, or provides an alternative to, the powerup-sweep features discussed above.

The design of the tank 720 also benefits from alternative placement ofthe ultrasonic transducers 730 mounted with the tank. As illustrated,the transducers 730 are mounted to the sides 720 s of the tankdecreasing the disruption which might otherwise occur frombottom-mounted transducers interfering with the solution flow throughthe baffles 722, 724.

A common feature in prior art tanks (ultrasonic and non-ultrasonic) is aquick dump rinse feature (QDR) where a large valve in the bottom of thetank opens to allow the solution in the tank to quickly drain out of thetank. This QDR feature reduces the contamination residing on the partsunder process as compared to the contamination that would reside if theliquid were removed more slowly from the tank, or if the parts werepulled out of the tank.

FIG. 48 illustrates a QDR tank 800 modified in accord with the inventionto speed up the rate of liquid removal from the tank. The large valveoutput 802 is connected to a vacuum reservoir 806 that is evacuated to apressure below atmospheric pressure during the cleaning cycle. When thevalve 802 is opened to dump the liquid 702″, the difference betweenatmospheric pressure and the pressure in the vacuum vessel 806 forcesthe liquid 702″ out of the tank 800, thus shortening the drain time andfurther reducing the residual contamination.

The conventional stacked transducer consists of a front driver, activepiezoelectric elements and a back mass. The length “L” of the transducer(from front plate to backplate) basically determines the transducer'sprimary and harmonic frequencies. As the fundamental frequency of thetransducer becomes higher, the thickness of each of the transducerelements is reduced until they become impractical. FIG. 49 shows atransducer 850 constructed according to the invention which reduces thisimpracticality.

In FIG. 49, the transducer 850 is shown connected to an ultrasoundprocessing tank 852, which holds process chemistry 854. The transducerincludes two piezoelectric elements 856 that are compressed between thebackplate 858 and the tank 852. Specifically, a bias bolt 860 connectsthrough the transducer 850 and connects directly into a weld 861 at thetank 852. Accordingly, there is no front plate; and thus the transducerlength “L” can be divided between the piezoelectric elements 856 and theback mass 858. This division makes it possible to make a stackedtransducer 850 with a higher fundamental frequency (and higher harmonicstoo).

Most transducers discussed herein are longitudinal vibrators withelements sandwiched by a center bolt that holds the transducer assemblytogether and that provides a compressive bias to the activepiezoelectric components (i.e., sandwiched between the a front plate andback mass or backplate). Since piezoelectric ceramic is strong undercompression, but weak in tension, the constant compressive forceprovided by the spring constant of the bolt greatly improves thereliability of this transducer over other configurations.

The longitudinal vibrating transducer is normally connected to the tankor other surface that is to receive the sound energy by epoxy orbrazing, or by a mechanical stud, or by a combination of these schemes.

The invention of FIG. 50 illustrates a transducer 900 constructedaccording to the invention and shown in an exploded view. The transducer900 has “double compression”, as discussed below, to increase itsreliability over the prior art. Specifically, the bias bolt 904 has athrough-hole 902 in its center. The center hole 902 receives a secondbolt 906 that is welded to the surface of the tank 908 (illustrated byweld joint 927). When integrated, the second bolt 906 protrudes out pastthe tail mass 910 (i.e., the backplate) of the transducer 900 by way ofa Belleville disc spring washer 912 and nut 914, which screws onto bolt906.

As in other transducers herein, the transducer 900 includespiezoelectric ceramics 916, associated electrodes 918, and lead-outs 920for the electrodes 918.

The bias bolt 904 thus provides the first compressive force similar toother transducers herein. That is, the bolt 904 slides through the frontdriver 922 via the through-hole 924, and continues on through theceramics 916. The back mass 910 has threads 910 a which mate with thebolt 904; and thus the bolt 904 screws into the back mass 910. Bytightening the bolt 904 into the back mass 910, the bolt 904 firmlyseats into the counter-sink 922 a of the front plate 922 and compressionis applied to the ceramics 916.

As an alternative, the threads in the back mass 910 can be thru-holed;and a nut against the back mass can replace the threads to supportcompression bias on the piezoceramic 916.

The second compressive force derives from the operation of the secondbolt 906, which compresses the epoxy 926 after seating within thecounter-sink 904 a of the first bolt 904 and after tightening the nut914 onto the bolt 906. The front driver 922 is then bonded to the tank908 via an epoxy layer 926. The second compressive force keeps acompressive bias on the epoxy 926 bond between the front driver 922 andthe tank surface 908.

As an alternative, it is possible to eliminate the Belleville discspring washer 912 and rely entirely on the spring tension in the secondbolt 906; but the added feature of the Belleville disc spring washer 912provides a larger displacement before tension goes to zero.

The second compressive bias of transducer 900 provides at least threeimprovements over the prior art. First, during the epoxy curing process,the bias keeps force on the epoxy bond 926 (even if the epoxy layerthickness changes during a liquid state) resulting in a superior bond.Second, during operation of the transducer 900, the reliability of thebond 926 is enhanced because of the constant mechanical compressiveforce. That is, epoxy bonds are weakest in shear forces, and reasonablystrong in tension but superior in compression. Third, during abnormalconditions (e.g., a mechanical jar to the bonding surface) that mightdislodge a conventionally bonded transducer, the second compressionforce with its spring characteristics absorbs the mechanical shock andprotects the epoxy bond.

Those skilled in the art should appreciate that the double compressiontransducer 900 provides increased reliability when mounted with most anysurface, and not simply an ultrasonic tank 908.

FIG. 51 shows a cross-sectional view of a conventional stackedtransducer 1000 with a bias bolt 1002 that screws into threads 1004 inthe aluminum front driver 1006. The threads 1004 are only within the topportion 1006 a of the front driver 1006. The transducer includes thenormal piezo-ceramics 1007, electrodes 1008, and rear mass 1009.

FIG. 52 shows an alternative transducer 1010 constructed according tothe invention. In transducer 1010, the threads 1012 within the frontdriver 1014 are at bottom portion 1014 a so that bias pressure is notconcentrated on the top threads (as in FIG. 51) where the surface of thealuminum can be deformed in operation, decreasing bias pressure. Theelements 1002′, 1007′, 1008′ and 1009′ have similar function as in FIG.51; except that they are sized and shaped appropriately to accommodatethe thread repositioning at the bottom 1014 a of the driver 1014.

FIG. 53 illustrates a transducer 1020 that is similar to the transducer1010, FIG. 52, except that a helical insert 1022 is used instead of thethreads 1012. The helical insert 1022 is preferably made from steel andwill not plastically deform under normal transducer stresses. Thehelical insert 1022 thus prevents distortion of the aluminum driver1014′ under the normal stresses of the transducer 1020. Note that the ahelical insert can similarly replace the threads 1004 of the prior arttransducer 1000 to provide similar advantages in preventing distortion.

FIG. 54 illustrates a side view of one embodiment of the inventionincluding a 5 printed circuit board (PCB) 1030 connected with ultrasonictransducers 1032 such as described herein (including, for example,piezoelectric ceramics 1034). The PCB 1030 contains circuitry and wiringso as to function as an ultrasonic generator and for the electrodes ofthe transducers 1032. As such, the PCB 1030 can drive the transducers1032 to produce ultrasound 1036 when powered. By way of example, the PCB1030 can include the circuitry of FIG. 31.

The PCB 1030 and transducers 1032 are also substantially “integral” inconstruction so as to be a single unit. This provides structuralintegrity, and reduces the cost and size of the system.

FIG. 55 shows a top view of the PCB 1030 of FIG. 54. For purposes ofillustration, the top surface 1030 a of the PCB 1030 is shown withelectrodes 1038 for the positive side of the piezoelectric ceramic 1034.The electrodes 1038 are preferably connected by wiring 1048 (e.g.,circuit board land patterns) to provide for common voltage input to thetransducers 1032. There is a similar electrode pattern on the bottomside (not shown) of the PCB 1030 that makes contact with thetransducer's front driver 1032 b, which is in electrical contact withthe bias bolt 1032 a (FIG. 54). The bolt 1032 a connects through thetransducer 1032 and into the back mass 1032 c, providing electricalfeedthrough to the negative electrode of the piezoelectric ceramic 1034.The PCB 1030 thus provides two electrodes for each transducer 1032 andall the interconnect wiring for the transducers 1032 such as by etchingthe PCB pattern. The ultrasonic generator is also provided with the PCB1030 circuitry (illustrated by circuit board components 1040) with itsoutput connected into the transducer electrodes as part of the PCBartwork.

FIG. 56 illustrates an acid resistant transducer 1050 with internalpiezoelectric compression. By way of background, the above descriptionhas described certain transducers that utilize metal masses to lower theresonant frequency of the piezoelectric ceramics and a bolt to keep acompressive bias on the piezoelectric elements. In harsh environments,e.g., sulfuric acid process tanks, the metallic elements of thetransducer are prone to acid attack and therefore are a reliabilityrisk. The transducer 1050 of FIG. 56 resolves this problem byeliminating the metal masses and the bolt. The compressive force on thepiezoelectric ceramic 1058 is obtained by an epoxy 1052 that contractsupon curing. The metal “back mass” and the metal “front driver” such asdescribed above are replaced by a non-metallic material 1060. In FIG.56, the front driver 1060 a and back mass 1060 b are thus both made froma non-metallic material such as quartz.

The internal piezoceramics 1058 connect to wiring to drive the elements1058 in the normal way. To protect the wiring and ceramics, it can bemade from Teflon which is soldered to the ceramic 1058 by known methods,such as illustrated by solder joint 1064.

FIG. 57 illustrates a generator circuit 2000 used to implement powerup-sweep such as described herein (e.g., such as described in connectionwith FIG. 31, except that FIG. 31 uses IGBT's as the switching devicesand FIG. 57 uses MOSFET's). In FIG. 57, circuit 2000 includes acapacitive element 2012 with terminal 2012 a connected to earth ground2015 a The other terminal 2012 b connects to terminal 2040 b of inductor2040. Terminal 2040 a of inductor 2040 connects to terminal 2013 a ofthe secondary 2013 c of transformer 2013. Terminal 2013 b of secondary2013 c connects to earth ground 2015 b. The circuit 2000 includes twodrive networks 2018 and 2020, and a controller 2022.

Drive network 2018 includes a blocking network 2028 and a multi-statepower switch network 2030, which is coupled to the controller 2022 byway of line 2022 a. The drive network 2020 includes a blocking network2032 and a multi-state power switch network 2034, which is coupled tothe controller 2022 by way of line 2022 b.

In drive network 2018, the blocking network 2028 and switch network 2030provide a unidirectional current flow path characterized by a firstimpedance from the potential +V through the first primary winding 2013 d1 of center-tapped primary winding 2013 d of transformer 2013 when theswitch network 2030 is in a first (conductive) state. The networks 2028and 2030 provide an oppositely directed current flow path characterizedby a second impedance from circuit ground 2023 a through 2013 d 1 to thepotential +V when the switch network 2030 is in a second(non-conductive) state. The first impedance of the flow path establishedwhen network 2030 is in its first state is lower than the secondimpedance of the flow path established when the network 2030 is in itssecond state.

In drive network 2020, the blocking network 2032 and switch network 2034provide a unidirectional current flow path characterized by a thirdimpedance from the potential +V through the second primary winding 2013d 2 of center-tapped primary winding 2013 d of transformer 2013 when theswitch network 2032 is in a first (conductive) state. The networks 2032and 2034 provide an oppositely directed current flow path characterizedby a fourth impedance from circuit ground 2023 b through 2013 d 2 to thepotential +V when the switch network 2034 is in a second(non-conductive) state. The third impedance of the flow path establishedwhen network 2034 is in its first state is lower than the fourthimpedance of the flow path established when the network 2030 is in itssecond state.

The impedance (Z) of drive network 2018 when switch network 2030 is inits second state may be primarily determined by resistor 2028 b (ofvalue “R”), in which case Z has a value substantially equal to R forcurrent flow in a direction toward +V, and a “near-infinity” value (i.e.relatively high) for current flow away from +V. In other embodiments, Zmay be non-linear, normally lower at the beginning of operation in thesecond state and higher at times after the second state begins. Forexample, a metal oxide varistor (MOV) in parallel with a resistor (R)may be the primary determining factor for Z. In this case, at thebeginning of operation in the second state when the voltage across Z ishigh, the low impedance of the on MOV primarily determines Z and laterin the second state, as the voltage drops below the MOV's breakdownpotential, Z is primarily determined by R.

A similar situation occurs for the impedance of drive network 2020 whenswitch network 2034 is in its second state.

Where the circuit 2000 is adapted to drive an ultrasonic transducer, thecapacitive element 2012 may be an electrostrictive device suitable foruse as an ultrasonic transducer. With such a configuration, for example,the controller 2022 may effectively control the circuit 2000 to drivesuch ultrasonic transducers at a selectively controlled frequency. Invarious forms of the invention, the controller 2022 may be adaptivelycontrolled so as to track variations in the resonant frequency for therespective ultrasonic transducers, or to frequency modulate thefrequency with a function such as a power up-sweep function, describedabove.

In operation, the controller 2022 cyclically switches the switch network2030 between its first and second states at a frequency f (f=1/T), wheref is less than or equal to f_(r) (f_(r)=1/T_(r)), where f_(r) is theresonant frequency of the series LC network formed by 2012 and 2040,approximately equal to 1/(2π(LC)^^(1/2)). During each cycle, network2030 is controlled to be in its first state for a period greater than orequal to T_(i)/2, but less than or equal to T/2, at the beginning ofeach cycle. Network 2030 is controlled to be in its second state for theremainder of each cycle.

Similarly, the controller 2022 also cyclically switches the switchnetwork 2032 between its first and second states at the frequency f(f=1/T). During each cycle, network 2032 is controlled to be in itsfirst state for a period greater than or equal to T_(i)/2, but less thanor equal to T/2, at the beginning of each cycle. Network 2032 iscontrolled to be in its second state for the remainder of each cycle. Inthe presently described embodiment, the start time for each cycle of theswitching of network 2030 is offset by T/2 from the start time for eachcycle of the switching of network 2034. In other forms, the start timefor the cycle of the switching network 2030 may be offset by at leastT_(r)/2 and less than T_(r)/2+D, where D equals T−T_(r).

An AC voltage waveform (V₀) at frequency f is impressed across thecapacitive element 2012. Generally, this voltage waveform V₀ passes fromlow to high and from high to low with a sinusoidal waveshape (atfrequency f_(r)). After rising from its low peak level to its high peaklevel, the voltage waveform stays substantially at its high peak level(except for droop due to resistive losses) for a period ½ (T−T_(r)), orD/2, before passing from that high peak level to its low peak level.Similarly, upon returning to the low peak level, the voltage waveform V₀remains at that level (except for droop due to resistive losses) for aperiod ½ (T−T_(r)), or D/2, before again passing to the high peak level.

Thus, the voltage impressed across capacitive element 2012 rises andfalls at the resonant frequency f_(r) with the capacitive element 2012being maintained in its fully charged state for a “dead” time which isadjustably dependent upon the switching frequency f of the controller2022. Accordingly, the drive frequency to the element 2012 may beadjustably controlled.

Where the element 2012 is an ultrasonic transducer, circuit 2000 is usedto drive that transducer at a frequency adjusted to match the optimaldrive frequency. In various embodiments, variations in that optimaldrive frequency may be detected and the controller may be adjusted inclosed loop fashion to adaptively track such variations.

Blocking network 2028 includes a diode 2028 a in parallel with aresistor 2028 b, and the blocking network 2032 includes a diode 2032 aand a resistor 2032 b. The single inductor (L) 2040 operates inresonance with the element 2012.

Circuit 2000 is particularly useful with “fast” switching devices (suchas bipolar, MOS and IGBT transistors) which do not require an extendedturnoff time. In operation, the capacitive element 2012 and transformer2013 function like the circuit of FIG. 31, except that circuit 2000utilizes FETs instead of IGBTs (insulated gate bipolar transistors) forthe terminal power switching devices. The power devices 2030, 2034 arealso connected to circuit ground, eliminating the need for separateisolated power supplies, reducing the cost of the generator.

In another implementation of circuit 2000, FIG. 57, the inductor 2040 isnot a separate component, but rather is incorporated into thetransformer 2013 by way of leakage inductance. This leakage inductanceperforms the same function as inductor 2040 and the leakage inductanceis controlled by the coupling of transformer 2013, e.g., by setting agap in the transformer's core as is known in the art.

With further reference to FIG. 33, one embodiment of the inventioncouples multiple generator frequencies to a common tank 306′ andtransducers 304′. FIG. 58 schematically shows additional switchcircuitry 2098 compatible with this embodiment In FIG. 58, a common 24VDC supply 2100 couples to a user-selectable switch 2102 (e.g., a rotaryswitch) to provide drive energy to remote connectors 2104 a–d (eachconnector 2104 corresponding and connecting to a different generatorfrequency, e.g., 2104 a for 40 khz, 2104 b for 72 khz, 2104 c for 104khz, and 2104 d for 170 khz). Which ever generator thus connects to the24 VDC supply between pins “1” and “2” on its corresponding remoteconnector 2104 will drive the common process tank, as shown in FIG. 59.The generators can have a remote on/off relay in the form of FIG. 60,which illustrates coupling between a Deltrol relay and the remove relay.The connector-to-tank wiring is further illustrated in FIG. 59. In FIG.59, each generator within the system connects to each of the pluralityof transducers 2106 within the tank; though only one generator activelydrives the transducers 2106 depending upon the position of the switch2102.

In operation, power is applied to one generator (e.g., the 40 khzgenerator coupled to remote connector 2104 a) via the 24VDC signal fromthe rotary switch 2102. The following sequence then occurs with respectto FIGS. 58–60:

Time Event   7 milliseconds Remote relay #1 energizes starting the 1/2sec. timer #1  10 milliseconds Deltrol relay #1 connects the tank to the40 khz generator 0.5 seconds 1/2 sec. timer #1 starts the 40 khzgenerator, the tank runs at 40 khz

If the rotary switch 2102 is turned to the next position, e.g., to the72 khz generator position, the following sequence occurs (assuming,worst case, that the rotary switch is moved very fast so there is zerotime between the 40 khz position and the 72 khz position):

Time Event   0 milliseconds 24VDC is removed from remote relay #1   0milliseconds 24VDC is removed from Deltrol relay #1   5 milliseconds 40khz generator turns off   7 milliseconds 72 khz remote relay #2energizes starting the 1/2 sec. timer #2   10 milliseconds Deltrol relay#2 connects tank to 72 khz generator  250 milliseconds Deltrol relay #1disconnects 40 khz generator from the tank  0.5 seconds 1/2 sec. timer#2 starts the 72 khz generator, the tank runs at 72 khz

To avoid this “worst case” scenario, extra margin is provided byproviding an off position between each rotary switch generator position.That is, the rotary switch can be labeled as follows:OFF-40 khz-OFF-72 khz-OFF-104 khz-OFF-170 khz

Generators connected within this system preferably have a four socketreverse sex square flange AMP CPC receptacle with arrangement 11-4 (AMPpart number 206430-1) installed on the rear of the generator. The matingfour pin plug (AMP part number 206429-1) has the following pinconnections:

Pin#1 +24 VDC referenced to Pin #2 connects the generator or powermodule to the transducers and turns the generator on Pin#2 return for 24VDC signal, can be grounded Pin#3 anode of LED to indicate RF currentflow Pin#4 cathode of LED to indicate RF current flow

The cable from the AMP plug is for example a Manhattan/Cot PIN M39025control cable with four #24 AWG wires, with the following color codes:Pin#1 red; Pin#2 green; Pin#3 blue; and Pin#4 white.

Generators within this system can have a nine socket reverse sex squareflange AMP CPC receptacle with arrangement 17-9 (AMP part number211769-1) installed on the rear of the generator according to thefollowing connections.

-   -   Socket #1: +RF output    -   Socket #2: not used    -   Socket #3: +RF output    -   Socket #4: −DC test point    -   Socket #5: −RF output, ground    -   Socket #6: cable shield, ground    -   Socket #7: +DC output interlock    -   Socket #8: +DC input interlock    -   Socket #9: waveform test point

The mating nine pin plug (AMP part number 211768-1) can have thefollowing pin outs and color code when supplied with a three wire RFcable.

-   Pin#1: +RF output red-   Pin#3: +RF output red-   Pin#5: −RF output green/yellow

All pin#5s can for example be wired together and connected to the −RFtransducer lead. All pin #1's are then connected together and connectedto the +RF transducer lead coming from one-half of the transducers. Allpin #3's are then connected together to the +RF transducer lead comingfrom the other one-half of the transducers. The only exception to thisis when the generators do not all drive the same number of transducers.

FIG. 61 schematically shows a multi-generator system 3000 used to drivecommon transducers 3002. One advantage of the system 3000 is thatmultiple generators 3004 can alternatively drive the transducer 3002;and it is assured that no two generators operate simultaneously. Eachgenerator 3004 preferably represents a different drive frequency.Generator 3004 a represents, for example, the generator set forth bycircuitry of FIG. 31 (except that preferably, a ½ second delay isinstalled into circuit 250 by adjusting capacitor 3006 to one microfaradinstead of 1/10 microfarad, which provides only 50 ms delay). The relays3008 a, 3008 b for example can be implemented similar to the relayschematic of FIG. 60.

The rotary switch 3010 (e.g., similar to the switch 2102, FIG. 58)permits user selection between any of the generators 3004. Generator3004 b can thus be switched in to drive the transducer 3002 with adifferent frequency. Those skilled in the art should appreciate thatadditional generators 3004 c, 3004 d, . . . can be installed into thesystem 3000 as desired, with additional frequencies. Those skilled inthe art should appreciate that the rotary switch 3010 can be replaced bya PLC or computer control to provide similar generator selection.

The invention thus attains the objects set forth above, among thoseapparent in the preceding description. Since certain changes may be madein the above description without departing from the scope of theinvention, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings be interpreted asillustrative and not in a limiting sense. It is also to be understoodthat the following claims are to cover all generic and specific featuresof the invention described herein, and all statements of the scope ofthe invention which, as a matter of language, might be said to falltherebetween.

In an ultrasonic or microsonic cleaning or processing liquid, it isknown that a particular frequency or a set of closely spaced frequencieswill resonate a certain size population of bubbles or voids within theliquid. A conventional sweeping frequency ultrasonic or microsoniccleaning or processing signal produces a particular frequency or a setof closely spaced frequencies followed by the next particular frequencyor set of closely spaced frequencies adjacent to the first particularfrequency or set of closely spaced frequencies.

Unfortunately, cavitation efficiency suffers with this type ofconventional sweeping frequency ultrasonic or microsonic cleaning orprocessing signal because the first particular frequency or set ofclosely spaced frequencies depletes members of that certain sizepopulation of bubbles or voids within the liquid leaving a smallerpopulation for the second adjacent particular frequency or set ofclosely spaced frequencies to resonate.

There is shown in FIG. 62, a sweeping frequency drive signal 3100 thatovercomes the above-described cavitation efficiency limitation of theprior art. When a certain size population of bubbles or voids within theliquid begins to be depleted causing a loss in cavitation efficiency,drive signal 3100 jumps, changes or rapidly sweeps to a non adjacentfrequency within the bandwidth of the transducer array, such that theprocess continues with improved cavitation allowed by the new bubblepopulation associated with this new non adjacent particular frequency orset of closely spaced frequencies.

In a preferred embodiment, drive signal 3100 can be maintained in theupper half of a bandwidth. The bandwidth is typically 10% of the centerfrequency (unless the system employs a special design / procedure, e.g.,overlapping transducers frequency ranges). Therefore, for a centerfrequency at the high end of the microsonic frequency range (350 kHz),the bandwidth is typically 35 kHz. For 40 kHz ultrasonic transducers,the bandwidth is typically about 4 kHz. After a defined period of time(i.e., before cavitation efficiency suffers) at point 3102, thefrequency is changed to a new frequency that is typically one halfbandwidth lower than the current frequency. This change in frequency mayoccur by sweeping the frequency to the new lower frequency (not shown;wherein the sweep time is typically less than 25% of the defined periodof time), or stepping the frequency to the new lower frequency, as shownin FIG. 62. The length of this “defined period of time” is dependent onthe frequency, power density, sweep rate, type of chemistry andchemistry conditions such as temperature. “Defined periods of time” varyinversely with respect to frequency and span the range from tenmicroseconds to two milliseconds. At point 3104, this sweeping frequencycontinues from this new lower frequency. After the defined period oftime (described above) at point 3106, the frequency jumps to a newhigher frequency (point 3108) that is typically one half bandwidthhigher than the current frequency.

While a one half bandwidth frequency jump is typical, other amounts arepossible. For example, the frequency may be jumped by a much largerpercentage of the bandwidth, e.g., to a frequency proximate the lowerlimit of the bandwidth, such as point 3109.

Further, while the system is described above as sweeping the frequencybetween points 3104 and 3106, other configurations are possible. Forexample, the frequency maybe maintained constant (not shown) during thedefined period of time. Alternatively, the frequency may be changed(between points 3104 and 3106) via one or more frequency steps (shown inphantom); or the set of closely spaced frequencies between points 3104and 3106 may be random frequencies (not shown).

This frequency sweeping and frequency jumping continues until strikingthe lowest frequency in the bandwidth (at point 3110). At this point,the frequency jumps to the highest frequency in the bandwidth (to point3112), and the sweeping and jumping process is repeated until the lowestfrequency in the bandwidth is reached again (not shown). This highcavitation efficiency process is repeated and continued for the timeneeded in that particular bandwidth.

If a multiple generator system is driving a transducer array with a setof defined bandwidths (e.g., multiple harmonic bandwidths), then afterthe time needed in a particular bandwidth has elapsed, the drive signalfrom a different generator may produce a similar high cavitationefficiency signal in a different bandwidth.

1. A multi-generator system for producing ultrasound at selecteddifferent frequencies within a processing tank of the type including oneor more transducers, comprising: a generator section having a firstgenerator circuit for producing first ultrasonic drive signals over afirst range of frequencies and a second generator circuit for producingsecond ultrasonic drive signals over a second range of frequencies, thegenerator section having an output unit connecting the drive signals tothe transducers, each generator circuit having a first relay initiatedby a user-selected command wherein either the first or the second drivesignals are connected to the output unit selectively.
 2. A system ofclaim 1 further comprising a 24 VDC supply to provide power for therelays.
 3. A system of claim 1, each generator circuit furthercomprising a second relay for energizing the circuit, and furthercomprising two time delay circuits, the first time delay circuitdelaying generator circuit operation over a first delay period from whenthe second relay is energized, the second time delay circuit delayingdiscontinuance of the first relay over a second delay period after thegenerator circuit is commanded to stop, the first delay period beinglonger than the second delay period such that no two generators circuitsoperate simultaneously and such that all generator circuits are inactiveduring switching of the first relay.
 4. A system of claim 3, furthercomprising one of a PLC, a computer, or a selector switch for selectingan operating generator circuit by way of supplying a reference voltageto the two relays of the operating generator circuit.
 5. A system ofclaim 4, wherein each relay operates at a common reference voltage.
 6. Amulti-generator system for producing ultrasound at selected differentfrequencies within a processing tank, comprising: a generator sectionhaving: a first generator circuit for producing first ultrasonic drivesignals over a first range of frequencies; and a second generatorcircuit for producing second ultrasonic drive signals over a secondrange of frequencies; wherein the generator section includes an outputunit for providing the drive signals to one or more devices, and eachgenerator circuit includes a first relay initiated by a user-selectedcommand, wherein either the first or the second drive signals areconnected to the output unit selectively.
 7. A system of claim 6 furthercomprising a 24 VDC supply to provide power for the relays.
 8. A systemof claim 6, each generator circuit further comprising a second relay forenergizing the circuit, and further comprising two time delay circuits,the first time delay circuit delaying generator circuit operation over afirst delay period from when the second relay is energized, the secondtime delay circuit delaying discontinuance of the first relay over asecond delay period after the generator circuit is commanded to stop,the first delay period being longer than the second delay period suchthat no two generators circuits operate simultaneously and such that allgenerator circuits are inactive during switching of the first relay. 9.A system of claim 8, further comprising one of a PLC, a computer, or aselector switch for selecting an operating generator circuit by way ofsupplying a reference voltage to the two relays of the operatinggenerator circuit.
 10. A system of claim 9, wherein each relay operatesat a common reference voltage.
 11. A system of claim 6 wherein themulti-generator system is configured to produce ultrasound within a setof defined bandwidths, and one or more of the generator circuits isconfigured to: sweep the drive signal from a first frequency to a secondfrequency during a first defined time period; switch the frequency ofthe drive signal from the second frequency to a third frequency; andsweep the drive signal from the third frequency to a fourth frequencyduring a second defined time period; wherein the third frequency isapproximately one half bandwidth less than the second frequency.
 12. Amulti-frequency transducer array capable of producing ultrasound atselected different frequencies within a processing tank, comprising: afirst and second transducer for receiving either a first ultrasonicdrive signal over a first range of frequencies or a second ultrasonicdrive signal over a second range of frequencies; wherein the firstultrasonic drive signal results in the first and second transducerproducing ultrasound throughout the first range of frequencies; andwherein the second ultrasonic drive signal results in the first andsecond transducer producing ultrasound throughout the second range offrequencies.
 13. A system of claim 12 further comprising one or moreadditional transducers for receiving either the first ultrasonic drivesignal or the second ultrasonic drive signal.
 14. A system of claim 12,further comprising a generator section having a first generator circuitfor producing the first ultrasonic drive signal and a second generatorcircuit for producing the second ultrasonic drive signal, the generatorsection having an output unit connecting the drive signals to thetransducers, each generator circuit having a first relay initiated by auser-selected command wherein either the first or the second drivesignals are connected to the output unit selectively.
 15. A system ofclaim 14 further comprising a 24 VDC supply to provide power for therelays.
 16. A system of claim 14, each generator circuit furthercomprising a second relay for energizing the circuit, and furthercomprising two time delay circuits, the first time delay circuitdelaying generator circuit operation over a first delay period from whenthe second relay is energized, the second time delay circuit delayingdiscontinuance of the first relay over a second delay period after thegenerator circuit is commanded to stop, the first delay period beinglonger than the second delay period such that no two generators circuitsoperate simultaneously and such that all generator circuits are inactiveduring switching of the first relay.
 17. A system of claim 16, furthercomprising one of a PLC, a computer, or a selector switch for selectingan operating generator circuit by way of supplying a reference voltageto the two relays of the operating generator circuit.
 18. A system ofclaim 17, wherein each relay operates at a common reference voltage. 19.A system of claim 14 wherein the multi-frequency transducer array iscapable of producing ultrasound across a set of defined bandwidths, andone or more of the generator circuits is configured to: sweep the drivesignal from a first frequency to a second frequency during a firstdefined time period; switch the frequency of the drive signal from thesecond frequency to a third frequency; and sweep the drive signal fromthe third frequency to a fourth frequency during a second defined timeperiod; wherein the third frequency is approximately one half bandwidthless than the second frequency.